Standards Compliance

Ibex is a standards-compliant 32 bit RISC-V processor. It follows these specifications:

• RISC-V Instruction Set Manual, Volume I: User-Level ISA, document version 20190608-Base-Ratified (June 8, 2019)

• RISC-V Instruction Set Manual, Volume II: Privileged Architecture, document version 20211203 (December 4, 2021). Ibex implements the Machine ISA version 1.12.

• RISC-V External Debug Support, version 0.13.2

• RISC-V Bit-Manipulation Extension, version 1.0.0 and version 0.93 (draft from January 10, 2021)

• PMP Enhancements for memory access and execution prevention on Machine mode (Smepmp) version 1.0

Many features in the RISC-V specification are optional, and Ibex can be parametrized to enable or disable some of them.

Ibex can be parametrized to support either of the following two instruction sets.

• The RV32I Base Integer Instruction Set, version 2.1

• The RV32E Base Integer Instruction Set, version 1.9 (draft from June 8, 2019)

In addition, the following instruction set extensions are available.

Table 1 Ibex Instruction Set Extensions

Extension	Version	Configurability
C: Standard Extension for Compressed Instructions	2.0	always enabled
M: Standard Extension for Integer Multiplication and Division	2.0	optional
B: Standard Extension for Bit-Manipulation Instructions	1.0.0 + 0.93 1	optional
Zicsr: Control and Status Register Instructions	2.0	always enabled
Zifencei: Instruction-Fetch Fence	2.0	always enabled
Smepmp - PMP Enhancements for memory access and execution prevention on Machine mode	1.0	always enabled in configurations with PMP see PMP Enhancements

Ibex currently supports the following features according to the RISC-V Privileged Specification, version 1.12.

• M-Mode and U-Mode

• All CSRs listed in Control and Status Registers

• Performance counters as described in Performance Counters

• Vectorized trap handling as described at Exceptions and Interrupts

Footnotes

1

Ibex fully implements the ratified version 1.0.0 of the RISC-V Bit-Manipulation Extension including the Zba, Zbb, Zbc and Zbs sub-extensions. In addition, Ibex also supports the remaining Zbe, Zbf, Zbp, Zbr and Zbt sub-extensions as defined in draft version 0.93 of the RISC-V Bit-Manipulation Extension. Note that the latter sub-extensions may change before being ratified as a standard by the RISC-V Foundation. Ibex will be updated to match future versions of the specification. Prior to ratification this may involve backwards incompatible changes. Additionally, neither GCC or Clang have committed to maintaining support upstream for unratified versions of the specification.